German Patent Publication No. DE 25 05 587 C3 discloses a length measuring instrument in which a scale is secured by an angle bracket to one of the objects to be measured and a scanner device is secured to the second object by a mounting foot. The angle bracket has a weak point in the form of a groove. The angle bracket allows a rotary motion of the scale about an axis at right angles to the measurement direction. To compensate for inaccuracies of guidance, a coupling is provided between the mounting foot and the scanner device. The scanner device is guided on the scale.
German Patent Publication No. DE 31 13 962 A1 discloses a length measuring instrument that is rotatably supported about its longitudinal axis while it is being mounted. During measurement operation, rotatability is precluded since the ends are fixed in the final mounted position.
International Patent Application WO 91/03145 A1 describes a machine, such as a hexapod having telescoping arms. The relative location of two machine parts can be varied by the plurality of telescoping arms. The relative location can be determined by the instantaneous length of the telescoping arms. To that end, one length measuring instrument is provided in each telescoping arm. It comprises a rodlike round scale and a scanner unit.